If you get three quotes and give the job to whoever is cheapest, you probably deserve a cheap job.
Understand what development process the company will take you through and what you’ll get at the end of it. What browsers will the site work in? Will it work well on mobile devices and tablets? Is it responsive or crafted or neither? What will you be charged for hosting and for changes?
If you appoint the company who cold-call you without seeking out another two companies/freelancers to compare them to, you could get taken to the cleaners.
Some of the least reputable companies have the best sales forces. Spend enough time with each candidate to get a sense of how they do business.
If you don’t ask where the work is being done and by whom, you deserve to have the work done overseas without good quality control.
That’s not to say good work can’t be done overseas, but you should satisfy yourself the quality control will be up to speed. Work done overseas is usually cheaper, so that should be reflected in their quote.
If you don’t see previous examples of work the company/freelancer has done and you don’t personally talk to those referrals about how the development worked out, you deserve a web site built in outdated technology, delivered late.
If you know nothing about web development and you accept everything the web dev tells you without checking it, you deserve to pay three times as much as necessary for an over-engineered site that you can’t understand how to work.
If you’re not knowledgeable, consider employing someone to project manage on your behalf or at least find an advisor who has experience in the area.
If you use photos or graphics on your web site without getting permission from the owner you deserve the embarrassment of being outed for copyright violation.
If you pay for an SEO service without understanding what will be done on your behalf and how Google feels about that, you deserve to get thrown out of the index and lose 98% of your web traffic for months.
To sum up, clients need to do their research, ask intelligent, well-informed questions and stay close to the project. Or they risk a sub-standard, over-priced project.